An implantable medical device is a medical device that is implanted in a patient to, among other things, monitor electrical activity of a heart and to deliver appropriate electrical and/or drug therapy, as required. Implantable medical devices (IMDs) include, for example, pacemakers, cardioverters, defibrillators, and the like. The electrical therapy produced by an IMD may include, for example, pacing pulses, cardioverting pulses, and/or defibrillator pulses. The IMD is used to both provide treatment for the patient and to inform the patient and medical personnel of the physiologic condition of the patient and the status of the treatment.
In general, implantable medical devices include a battery and electronic circuitry, such as a pulse generator and/or a processor module, that are hermetically sealed within a metal housing (generally referred to as the “can”). The metal housing typically is formed of titanium and includes opposed concave half shells that are welded together to form a device housing with an interior cavity, in which the battery, pulse generator and/or processor module reside. The half shells have an oval contour with a header receptacle area configured to receive a header assembly that is joined to the device housing. A feed-through assembly is located at the header receptacle area and is sealed to the half shells of the device housing to form an interface for conductors to enter/exit the interior cavity.
During manufacture, the battery and electronic circuitry are encased between the opposed half shells of the device housing and the half shells are welded to one another, such as through the use of laser welding, to form the IMD. Following the laser welding process, argon and/or helium gas may remain within the interior of the device case. Argon and helium gas exhibit low breakdown voltage characteristics (e.g., 12 volts/mil for argon and 4 volts/mil for helium). Thus, it may be preferable to remove the argon or helium gas from the completed implantable medical device. To remove the argon and helium gas, the device is placed in a nitrogen chamber and nitrogen gas, which has a higher break-down voltage (e.g., 81 volts/mil), is back-filled into the device case through a back-fill port provided in the device case. Upon completion of the nitrogen back-filling process, the back-fill port is temporarily sealed. The device case is then removed from the nitrogen chamber and into the back-fill port is permanently sealed.
However, conventional implantable medical devices and methods of manufacture have experienced certain limitations. Conventional manufacturing methods for joining feed-through assemblies and back-fill ports to a device case are unduly complex and costly. Further, once the device is removed from the nitrogen chamber, the nitrogen gas may leak out around the temporary seal before being permanently sealed to the back-fill port. Also, when temporarily sealing the back-fill port, a support tool and a press tool are used. The support tool must fit into an area that has a very close tolerance, without interfering with the feed-through assembly, which makes the manufacturing process difficult, unpredictable and slow.
A need remains for an improved feed-through and back-fill configuration for an implantable medical device, and methods of manufacturer therefor.